794 XIII. ESSENTIAL FATTY ACIDS 



A method of synthesis which should prove useful for the preparation of 

 carboxyl-Iabeled linoleic acid has been recently announced by Howton and 

 co-workersJ^ In this procedure tetrabromstearic acid was produced by 

 bromination of natural linoleic acid. After decarboxylation of the silver 

 salt of the tetrabrom-acid with bromine, the compound Avas debrominated 

 with zinc, and the linoleic acid was regenerated with a new carboxyl group 

 by means of the Grignard reagent with CO2. 



Howton, Davis, and NevenzeP" synthesized 1-C'Minoleic acid as well 

 as 1-C^Minolenic acid. 



3. Bioassay of Essential Fatty Acids 

 (1) Growth Method of Greenherg and Co-Workers 



When weanling rats are fed diets complete in all essential dietary compo- 

 nents with the exception of the EFA, retardation of the growth of the animals 

 begins within several weeks, and the body weight reaches a plateau after 

 nine to ten weeks, according to Deuel et al.^^ From then on, the body 

 weight may remain fairly constant over an extended period of time, or it 

 may gradually decline, and the rats may succumb. If EFA are fed to the 

 depleted rats on a basal fat-free diet after a constant body weight has been 

 established, an increase in body weight promptly occurs. Within cer- 

 tain limits, the increase is proportional to the amount and potency of the 

 active compound employed. Greenberg and associates'^ reported that, 

 when the log dose of linoleate fed was plotted against the gain-in-weight 

 of male rats for doses of linoleate of 5, 10, 20, or 50 mg. per day, a straight- 

 line function occurred promptly at three weeks, and continued for as long 

 as twelve weeks, at which time the experiment was terminated. By com- 

 paring the gain-in-weight induced by a test substance fed at several levels 

 with that noted when standardized doses of linoleate are used, it is possible 

 to calculate the linoleate equivalent of the unknown. 



Although the rationale of the growth method is a sound one, since it 

 is based upon the same procedure as the one suggested by Cowai'd^^ for 



"•^D. R. Howton, R. H. Davis, and J. C. Nevenzel, ./. Am. Chem. Soc, 74, 1179 

 (1952). 



80 D. R. Howton, R. H. Davis, and J. C. Nevenzel, /. .4m. Chem. Soc, 76, 4970-4974 

 (1954); also unpublished data, 1954. 



81 H. J. Deuel, Jr., S. M. Greenberg, C. E. Calbert, E. E. Savage, and T. Fukui, J. 

 Nutrition, 40, 351-366 (1950). 



82 S. M. Greenberg, C. E. Calbert, E. E. Savage, and H. J. Deuel, Jr., J. Nutrition, 4I, 

 473-486(1950). 



83 K. H. Coward, The Biological Standardization of the Vitamins, 2nd ed., Williams & 

 Wilkins, Baltimore, 1947, pp. 35 ff. 



